Light sensor and ranging method

ABSTRACT

A light sensor and a ranging method are provided. The light sensor includes a light source, a sensing sub-pixel, and a control circuit. The sensing sub-pixel includes a diode. The control circuit operates the diode in a Geiger mode or an avalanche linear mode. The control circuit includes a time-to-digital converter. The control circuit sequentially delays multiple light emission times of the light source in consecutive multiple sensing periods according to delay times during the consecutive multiple sensing periods. The control circuit sequentially monitors whether multiple digital values sequentially outputted by the time-to-digital converter corresponding to the consecutive multiple sensing periods have changed. The control circuit calculates a distance value according to the multiple digital values and a corresponding delay sequence when the control circuit determined that the multiple digital values have changed for a first time.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of U.S. provisionalapplication Ser. No. 63/050,120, filed on Jul. 10, 2020, and U.S.provisional application Ser. No. 63/058,502, filed on Jul. 30, 2020. Theentirety of each of the above-mentioned patent applications is herebyincorporated by reference herein and made a part of this specification.

BACKGROUND Technical Field

This disclosure relates to a sensing technology, and in particular to alight sensor and a ranging method.

Description of Related Art

Currently, there is a high demand for high-sensitivity ranging sensorsin various application fields, such as the medical field or theautomotive field. In particular, a light sensor that may be used tosense extremely low light is currently one of the main sensor designsunder development. However, a ranging result of a ranging sensor islimited by a bin resolution (or also known as a counting resolution) ofa digital converter 330, and cannot provide a more precise rangingresult. In view of this, how to enable a light sensor to effectivelysense extremely low light while having high precision remains achallenge for those skilled in the art.

SUMMARY

This disclosure provides a light sensor and a ranging method, which canprovide a high-precision ranging result.

The light sensor of the disclosure includes a light source, a sensingsub-pixel, and a control circuit. The sensing sub-pixel includes adiode. The control circuit is coupled to the light source and thesensing sub-pixel, and is configured to operate the diode in a Geigermode or an avalanche linear mode. The control circuit includes atime-to-digital converter. The time-to-digital converter is coupled tothe diode. The control circuit sequentially delays multiple lightemission times of the light source in multiple consecutive sensingperiods according to multiple delay times during the multipleconsecutive sensing periods. The control circuit sequentially monitorswhether multiple digital values sequentially outputted by thetime-to-digital converter corresponding to the multiple sensing periodshave changed. The control circuit calculates a distance value accordingto the multiple digital values and a corresponding delay sequence whenthe control circuit determined that the multiple digital values havechanged for a first time.

The ranging method of the disclosure is applicable to a light sensor.The light sensor includes a light source, a sensing sub-pixel, and acontrol circuit. The sensing sub-pixel includes a diode. The controlcircuit includes a time-to-digital converter. The ranging methodincludes the following steps. The diode is operated in a Geiger mode oran avalanche linear mode through the control circuit. Multiple lightemission times of the light source in multiple consecutive sensingperiods are sequentially delayed through the control circuit accordingto multiple delay times during the multiple consecutive sensing periods.Whether multiple digital values sequentially outputted by thetime-to-digital converter corresponding to the multiple sensing periodshave changed is sequentially monitored through the control circuit. And,the control circuit calculates a distance value according to themultiple digital values and a corresponding delay sequence when thecontrol circuit determined that the multiple digital values have changedfor a first time.

Based on the above, the light sensor and the ranging method of thedisclosure may determine whether the sensing result corresponding to themultiple light emission times have changed according to the adjustmentof the multiple light emission times, so as to obtain the convertedresult with higher precision.

To make the above features and advantages more comprehensible, severalembodiments accompanied by drawings are described in detail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of a light sensor according toan embodiment of the disclosure.

FIG. 2 is a schematic diagram of a sensing array according to anembodiment of the disclosure.

FIG. 3 is a schematic circuit diagram of a sensing circuit according toan embodiment of the disclosure.

FIG. 4 is a characteristic curve diagram of a diode according to anembodiment of the disclosure.

FIG. 5 is a flowchart of a ranging method according to an embodiment ofthe disclosure.

FIG. 6 is an operation time sequence diagram of a light sensor accordingto an embodiment of the disclosure.

FIG. 7 is an operation time sequence diagram of a light sensor accordingto another embodiment of the disclosure.

DESCRIPTION OF THE EMBODIMENTS

In order to make the content of the disclosure more comprehensible, thefollowing embodiments are specifically cited as examples as to how thedisclosure may be implemented. In addition, wherever possible,elements/components/steps with the same reference numerals in thedrawings and the embodiments represent the same or similar components.

FIG. 1 is a schematic structural diagram of a light sensor according toan embodiment of the disclosure. FIG. 2 is a schematic diagram of asensing array according to an embodiment of the disclosure. Withreference to FIGS. 1 and 2, a light sensor 100 includes a controlcircuit 110, a sensing array 120, and a light source 130. The controlcircuit 110 is coupled to the sensing array 120 and the light source130. The sensing array 120 includes multiple sensing sub-pixels 121_1 to121_N, where N is a positive integer. Each of the sensing sub-pixels121_1 to 121_N includes at least one diode (photodiode). The diode maybe a pn junction diode. In the embodiment, the control circuit 110 maycontrol the sensing array 120 to operate the diodes in the sensingsub-pixels 121_1 to 121_N in a Geiger mode or an avalanche linear mode,so as to perform a light sensing operation.

In the embodiment, the light source 130 may be an infrared laser lightsource, but the disclosure is not limited thereto. In other embodimentsof the disclosure, the light source 130 may be a visible light source oran invisible light source. In the embodiment, the control circuit 110may respectively operate the multiple diodes of the sensing sub-pixels121_1 to 121_N in a single-photon avalanche diode (SPAD) state of theGeiger mode or the avalanche linear mode to sense a sensing light(pulsing light) emitted by the light source 130, thereby realizing aranging sensing function having a low light amount and a high sensingsensitivity characteristic.

In the embodiment, the control circuit 110 may be, for example, aninternal circuit or a chip of a light sensor, and includes digitalcircuit elements and/or analog circuit elements. The control circuit 110may control an operation mode of the diodes in the sensing sub-pixels121_1 to 121_N and/or an operation mode of the sensing sub-pixels 121_1to 121_N through changing a bias voltage of the diodes in the sensingsub-pixels 121_1 to 121_N and/or a control voltage of multipletransistors. The control circuit 110 may control the light source 130 toemit the sensing light, and may perform related signal processing andsensing data calculations on a sensing signal outputted by the sensingsub-pixels 121_1 to 121_N. In other embodiments of the disclosure, thecontrol circuit 110 may also be, for example, an external circuit or achip of a light sensor, for example, a processing circuit or a controlcircuit in a certain terminal device such as a central processing unit(CPU), a microprocessor control unit (MCU), or a field programmable gatearray (FPGA), but the disclosure is not limited thereto.

FIG. 3 is a schematic circuit diagram of a sensing circuit according toan embodiment of the disclosure. With reference to FIG. 3, a sensingcircuit 300 of the embodiment may be applicable to the control circuitand the sensing sub-pixel described in various embodiments of thedisclosure. In the embodiment, the sensing sub-pixel 300 includes adiode 310 and a cut-off resistor Rq. The control circuit includes anamplifier 320 and a time-to-digital converter 330. The time-to-digitalconverter 330 includes a count circuit 331. In the embodiment, a firstterminal of the diode 310 is coupled to a working voltage V_(OP)(V_(OP)=V_(BD)+V_(EB)), where V_(BD) is a breakdown voltage, and V_(EB)is an excess bias voltage. The cut-off resistor Rq is coupled between asecond terminal of the diode 310 and a ground terminal voltage. There isa node voltage V_(A) between the cut-off resistor Rq and the secondterminal of the diode 310. An input terminal of the amplifier 320 iscoupled to the second terminal of the diode 310. An output terminal ofthe amplifier 320 is coupled to the time-to-digital converter 330. Inthe embodiment, a control circuit (such as the control circuit 110 inFIG. 1) may control a bias voltage of the diode 310, to enable the diode310 to operate in the Geiger mode or the avalanche linear mode toreceive a ranging light emitted by a specific light source (such as thelight source 130 in FIG. 1). In this regard, the input terminal of theamplifier 320 may receive a sensing signal provided by the diode 310when the diode 310 sensed a single photon or several photons (tracephotons) of the ranging light. The sensing signal may be a single photonsensing signal. In addition, the output terminal of the amplifier 320may output an amplified sensing signal V_(OUT) to the time-to-digitalconverter 330. The amplified sensing signal V_(OUT) may be, for example,a square wave pulse signal.

FIG. 4 is a characteristic curve diagram of a diode according to anembodiment of the disclosure. With reference to FIGS. 1, 2 and 4, thediode of the sub-sensing pixel according to the embodiment may have acharacteristic curve 401 as shown in FIG. 4. A horizontal axis in FIG. 4is a bias voltage V of the diode, and a vertical axis is a current Ithat the diode may generate due to photoelectric conversion under acorresponding bias voltage. The diode may operate in a solar cell modewhen the bias voltage V of the diode is greater than 0 (a voltage rangeM1 as shown in FIG. 4). The diode may operate in a photodiode mode whenthe bias voltage V of the diode is between 0 and the avalanche breakdownvoltage V_APD (a voltage range M2 as shown in FIG. 4). The diode mayoperate in the avalanche linear mode when the bias voltage V of thediode is between the avalanche breakdown voltage V_APD and a breakdownvoltage V_SPAD (a voltage range M3 as shown in FIG. 4). The diode mayoperate in the Geiger mode when the bias voltage V of the diode is lessthan the breakdown voltage V_SPAD (a voltage range M4 as shown in FIG.4). In the embodiment, the control circuit 110 controls the biasvoltages of the multiple diodes of the sensing sub-pixel 121_1 to 121_N,so that the multiple diodes operate in the Geiger mode or the avalanchelinear mode to receive the sensing light emitted by the light source130.

FIG. 5 is a flowchart of a ranging method according to an embodiment ofthe disclosure. FIG. 6 is an operation time sequence diagram of thelight sensor 100 according to an embodiment of the disclosure. Withreference to FIGS. 1, 3, and 5, the light sensor 100 of the disclosuremay execute Steps S510 to S540 as follows to perform ranging. In theStep S510, the control circuit 110 may operate the diode 310 in theGeiger mode or the avalanche linear mode. In the Step S520, the controlcircuit 110 may sequentially delay multiple light emission times of thelight source 130 in multiple consecutive sensing periods according tomultiple delay times during the multiple consecutive sensing periods. Inthe Step S530, the control circuit 110 may sequentially monitors whethermultiple digital values sequentially outputted by the time-to-digitalconverter corresponding to the multiple sensing periods have changed.When the control circuit 110 determines that the multiple digital valueshave changed for a first time, in the Step S540, the control circuit 110may calculate a distance value according to the multiple digital valuesand a corresponding delay sequence.

For example, with reference to FIG. 6, the control circuit 110 maysequentially delay the multiple light emission times of the light source130 in the consecutive sensing periods according to delay times Td1 toTd10 during ten consecutive sensing periods. As shown in a count timesequence EP shown in FIG. 6, the control circuit 110 may operate thetime-to-digital converter 330 to respectively start performing a countoperation after a delay time length TA in each of the light emissiontimes. TA is a delay time of the circuit, and it may also be zero. Asshown in FIG. 6 in a preset light emission time sequence LP, presetlight emission times of the light source 130 have an interval of equaltime length. In this regard, as shown in an adjusted light emission timesequence LP′ shown in FIG. 6, the preset light emission times of thelight source 130 are respectively adjusted according to the delay timesTd1 to Td10, so that the light source 130 delays the emission. It shouldbe noted that the delay times Td1 to Td10 may be determined according toa (minimum) bin resolution (a sub-bin resolution or a sub-countingresolution) Tb of the time-to-digital converter 330. In this example,the delay time Td1 may be, for example, 1×Tb. The delay time Td2 may be,for example, 0.9×Tb. The delay time Td3 may be, for example, 0.8×Tb. Thedelay time Td4 may be, for example, 0.7×Tb. The delay time Td5 may be,for example, 0.6×Tb. The delay time Td6 may be, for example, 0.5×Tb. Thedelay time Td7 may be, for example, 0.4×Tb. The delay time Td8 may be,for example, 0.3×Tb. The delay time Td9 may be, for example, 0.2×Tb. Thedelay time Td10 may be, for example, 0.1×Tb. The delay times Td1 to Td10are less than the (minimum) bin resolution (counting resolution) Tb ofthe digital converter 330, therefore the disclosure may realize accuracyand precision of the sub-bin resolution.

In the example, the diode 310 may receive, for example, a reflectedlight of the sensing light emitted by the light source 130 and reflectedfrom a sensing target surface during the first to the sixth sensingperiods. Therefore, the time-to-digital converter 330 may output themultiple digital values corresponding to a first to a sixth distancesensing results according to count results of the first to the sixthsensing periods. The first to the sixth distance sensing results may allbe, for example, 91 milliseconds (ms). In addition, since the diode 310receives other multiple reflected lights of other multiple sensinglights emitted by the light source 130 and reflected from the sensingtarget surface during the seventh to the tenth sensing periods, thetime-to-digital converter 330 may output the multiple digital valuescorresponding to a seventh to a tenth distance sensing results accordingto multiple count results of the seventh to the tenth sensing periods.The seventh to the tenth distance sensing results may be, for example,90 milliseconds (ms). Therefore, the control circuit 110 may rely on,for example, the digital value and the delay sequence (the delaysequence of a seventh sensing period is 7, and a difference between thedelay in the seventh sensing period and the delay in the first sensingperiod is (7−1)×0.1 ms) corresponding to 91 milliseconds to calculatethe distance value when the control circuit 110 monitors that themultiple digital values obtained above have changed for a first timeduring the seventh sensing period. Taking time calculation as an example(actually it may be calculated using the digital value), the controlcircuit 110 may, for example, calculate a distance sensing result Daccording to a formula: D−6×0.1=91. Therefore, the control circuit 110may calculate the distance sensing result D=91+6×0.1=91.6 ms, where 0.1(0.1=1/10) is a reciprocal of total number of delays.

In this way, the control circuit 110 may obtain a sensing result that is10 times of the (minimum) bin resolution of the time-to-digitalconverter 330. In other words, the disclosure may realize the accuracyand precision of the sub-bin resolution. However, the sensing periodsand the number of delays in the disclosure are not limited to theabove-mentioned examples. The sensing periods of the disclosure and thenumber of delays of the light source 130 may be determined according toa multiplication of an expected to be obtained (minimum) bin resolutionof the digital converter 330. For example, if the expected binresolution is 100 times, the sensing periods and the number of delaysmay be 100 times respectively, so that the distance sensing resultcalculated by the control circuit 110 may be, for example, 91.65.Therefore, the light sensor 100 of the embodiment may provide ahigh-precision ranging result. For a general ranging circuit, a storagespace of the circuit is proportional to the resolution of the ranging.When the resolution is to be increased by 10 times, the storage space ofthe circuit has to be increased by 10 times. However, the disclosure mayincrease the resolution by, for example, 10 times or 100 times withoutincreasing the circuit storage space. From another perspective, thecontrol circuit 110 of the embodiment only has to monitor whether thedigital values outputted by the digital converter 330 change from timeto time, and calculate the distance value immediately when the digitalvalues have changed. In other words, since the control circuit 110 ofthe embodiment does not have to record the sensing results of each ofthe sensing periods, the light sensor 100 of the embodiment furtherobtains the high-precision ranging result in a storage space savingmeans.

FIG. 7 is an operation time sequence diagram of a light sensor accordingto another embodiment of the disclosure. With reference to FIGS. 1, 2,and 7, it should be noted that since the multiple diodes of the sensingsub-pixels 121_1 to 121_N respectively serve as the single-photonavalanche diodes (operating in the Geiger mode or the avalanche linearmode), when the multiple diodes respectively sense the photons and anavalanche event occurs, the sensing sub-pixels 121_1 to 121_N have torespectively re-bias the multiple diodes, causing there to be a periodof time (may be known as dead time) when the photons are unable to besensed. In this regard, in order to reduce impact of the dead time, thecontrol circuit 110 of the embodiment may, for example, set some of thesensing sub-pixels of the sensing sub-pixels 121_1 to 121_N of theembodiment as a sensing pixel (or macro-pixel). For example, withreference to FIG. 1, the four sensing sub-pixels 121_A to 121_D mayserve as a sensing pixel 122, where A to D are positive integers, andless than or equal to N. The control circuit 110 may determine whetherthe sensing sub-pixels 121_A to 121_D respectively sense one or morephotons in a corresponding same exposure time interval and concurrentlygenerate multiple sensing currents, to serve as a pixel sensing result.For example, the control circuit 110 may perform a calculation on thedistance sensing result (a time difference or a distance value) of thesensing sub-pixels 121_A to 121_D, to serve as the pixel sensing result.

Specifically, when the four diodes of the sensing sub-pixels 121_A to121_D are operating in the Geiger mode or the avalanche linear mode, thecontrol circuit 110 may sequentially expose the sensing sub-pixels 121_Ato 121_D belonging to the same pixel in a frame sensing period (that is,corresponding to the sensing period in the above-mentioned embodiment).That is, each of the sensing periods in the above-mentioned embodimentmay further include t0 to t6. Emission time sequences PH1 to PH4 of thesensing light are shown in FIG. 7, in which during the period from thetime t0 to the time t6, for example, there are four sensing lightsignals (photons) P1 to P4 being emitted to the sensing pixel 122.Exposure operation time sequences EP1 to EP4 are shown in FIG. 7, inwhich when the sensing sub-pixel 121_1 receives the sensing light signalP1 at the time t1 in an exposure period T1, the sensing sub-pixel 121_1may only proceed to perform the next exposure operation after a delaytime Td.

In this regard, if exposure periods T2 to T4 of the sensing sub-pixels121_2 to 121_4 are the same as the exposure period T1, then the sensingsub-pixels 121_1 to 121_4 may only receive the sensing light signal P1,and the sensing light signals P2 to P4 would not be sensed due to thesensing sub-pixels 121_1 to 121_4 being in the dead time.

Therefore, in the embodiment, an exposure starting time of the exposureperiods T2 to T4 of the sensing sub-pixels 121_2 to 1214 may berespectively sequentially delayed to the times t1 to t3, and twosequentially adjacent exposure periods of the exposure periods T1 to maypartially overlap. In this way, the sensing sub-pixel 121_2 may receivethe sensing light signal P2 between the time t1 and the time t2 in theexposure period T2. The sensing sub-pixel 121_3 may receive the sensinglight signal P3 between the time t3 and the time t4 in the exposureperiod T3. The sensing sub-pixel 121_4 may receive the sensing lightsignal P4 between the time t5 and the time t6 in the exposure period T4.Therefore, the sensing sub-pixel 121_2 to 121_4 may effectively receiveall of the sensing light signals P1 to P4 and provide accurate sensingresults.

In summary, the light sensor and the ranging method of the disclosuremay delay the multiple light emission times of the light sourceaccording to the delay times that are gradually changing, and calculatethe ranging results with higher precision according to the sensingresults of the light sensor corresponding to the multiple light emissiontimes. In addition, the light sensor and the ranging method of thedisclosure may also effectively reduce the impact of the dead time ofthe sensing sub-pixels and provide accurate sensing results.

Although the disclosure has been described with reference to theabove-mentioned embodiments, they are not intended to limit thedisclosure. It is apparent that any one of ordinary skill in the art maymake changes and modifications to the described embodiments withoutdeparting from the spirit and the scope of the disclosure. Accordingly,the scope of the disclosure is defined by the claims appended hereto andtheir equivalents in which all terms are meant in their broadestreasonable sense unless otherwise indicated.

What is claimed is:
 1. Alight sensor, comprising: a light source; asensing sub-pixel, comprising a diode; and a control circuit, coupled tothe light source and the sensing sub-pixel, and configured to operatethe diode in a Geiger mode or an avalanche linear mode, wherein thecontrol circuit comprises a time-to-digital converter, and thetime-to-digital converter is coupled to the diode, wherein the controlcircuit sequentially delays a plurality of light emission times of thelight source in a plurality of consecutive sensing periods according toa plurality of delay times during the plurality of consecutive sensingperiods, wherein the control circuit sequentially monitors whether aplurality of digital values sequentially outputted by thetime-to-digital converter corresponding to the plurality of sensingperiods have changed, wherein the control circuit calculates a distancevalue according to the plurality of digital values and a correspondingdelay sequence when the control circuit determined that the plurality ofdigital values have changed for a first time.
 2. The light sensoraccording to claim 1, wherein the plurality of delay times aresequentially decreased or increased at an equal time interval.
 3. Thelight sensor according to claim 1, wherein there is a delay time with alongest time length among the plurality of delay times, and a timelength of the delay time with the longest time length is equal to a timelength of one count bit of the time-to-digital converter.
 4. The lightsensor according to claim 1, wherein a time length difference betweenany two adjacent delay times among the plurality of delay times is lessthan a time length of one count bit of the time-to-digital converter. 5.The light sensor according to claim 1, further comprising at leastanother sensing sub-pixel, wherein the at least another sensingsub-pixel and the sensing sub-pixel belong to a same pixel, and thesensing sub-pixel and the at least another sensing sub-pixel aresequentially exposed in each of the plurality of sensing periods.
 6. Thelight sensor according to claim 5, wherein a plurality of exposureperiods of the sensing sub-pixel and the at least another sensingsub-pixel in the each of the plurality of sensing periods are partiallyoverlapped.
 7. A ranging method, suitable for a light sensor, the lightsensor comprising a light source, a sensing sub-pixel, and a controlcircuit, wherein the sensing sub-pixel comprises a diode, and thecontrol circuit comprises a time-to-digital converter, the rangingmethod comprising: operating the diode through the control circuit in aGeiger mode or an avalanche linear mode; sequentially delaying aplurality of light emission times of the light source in a plurality ofconsecutive sensing periods through the control circuit according to aplurality of delay times during the plurality of consecutive sensingperiods; sequentially monitoring whether a plurality of digital valuessequentially outputted by the time-to-digital converter corresponding tothe plurality of sensing periods have changed through the controlcircuit; and calculating a distance value according to the plurality ofdigital values and a corresponding delay sequence through the controlcircuit when the control circuit determined that the plurality ofdigital values have changed for a first time.
 8. The ranging methodaccording to claim 7, wherein the plurality of delay times aresequentially decreased or increased at an equal time interval.
 9. Theranging method according to claim 7, wherein there is a delay time witha longest time length among the plurality of delay times, and a timelength of the delay time with the longest time length is equal to a timelength of one count bit of the time-to-digital converter.
 10. Theranging method according to claim 7, wherein a time length differencebetween any two adjacent delay times among the plurality of delay timesis less than a time length of one count bit of the time-to-digitalconverter.
 11. The ranging method according to claim 7, furthercomprising at least another sensing sub-pixel, wherein the at leastanother sensing sub-pixel and the sensing sub-pixel belong to a samepixel, and the sensing sub-pixel and the at least another sensingsub-pixel are sequentially exposed in each of the plurality of sensingperiods.
 12. The ranging method according to claim 11, wherein aplurality of exposure periods of the sensing sub-pixel and the at leastanother sensing sub-pixel in the each of the plurality of sensingperiods are partially overlapped.